Diagnosing Clostridium difficile-associated diarrhea using enzyme immunoassay: the clinical significance of toxin negativity in glutamate dehydrogenase-positive patients Kazuhito Yuhashi,1 Yuka Yagihara,1 Yoshiki Misawa,1 Tomoaki Sato,1 Ryoichi Saito,2 Shu Okugawa,1 Kyoji Moriya1 1Department of Infection Control and Prevention, Faculty of Medicine, The University of Tokyo, 2Department of Microbiology and Immunity, Graduate School of Health Care Sciences, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan Purpose: The enzyme immunoassay (EIA) has lower sensitivity for Clostridium difficile toxins A and B than the polymerase chain reaction in the diagnosis of C. difficile-associated diarrhea (CDAD). Furthermore, toxin positivity with EIA performed on C. difficile isolates from stool cultures may be observed even in patients with EIA glutamate dehydrogenase (GDH)-positive and toxin-negative stool specimens. It is unclear whether such patients should be treated as having CDAD.Methods: The present study retrospectively compared patient characteristics, treatment, and diarrhea duration among three groups of patients who underwent stool EIA testing for CDAD diagnosis: a toxin-positive stool group (positive stool group;